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JSTOR helps people discover, use, and build upon a wide range of content through a powerful research and teaching platform, and preserves this content for future generations. JSTOR is part of ITHAKA, a not-for-profit organization that also includes Ithaka S+R and Portico. For more information about JSTOR, please contact email@example.com. 64 THE FERTILIZATIOX and respiratory functions, and their curious modes of reproduction must be deferred until the next number. explanation OF plate 3. Fredericella regina Leicly. Kg. 1, 2, and 3. Colonies attached to pieces of bark. Pig. i. Magnified view of one Polyzoon. D, brown envelope, the ectocyst; E, pellucid wall of the tube and cell, the endocyst; V, funiculus ; M, M', M", upper branches of the muscles, the retrac- tors ; N, N', muscles of the fold, the retentors ; F, a small infold- ing of the endocyst, the brachial collar; G, the pointed ruffle, or calyx ; H, the threads, or tentacles. Pig. 5. Outline of the interior of part of a young specimen. Same letters as above, with the exception of B, „ invaginated fold of the tube ; Y, a very young polyzoon, a bud ; K, the throat or oeso- phagus ; H", cilia surrounding the mouth ; K'", the valve opening into the stomach, oesophageal valve j_ K', stomach ; K"", intestinal valve partly open; K", intestine; K, opening of intestine, the anus; I, disc, the lophophore; I', the little flap, the epistome; I", the mouth ; S, nerve-mass. Kg. 6. Side view of the top of a cell, with the tube and crown drawn within ; letters same as before with the exception of A"", contracted orifice of the cell; L, position of muscular band, the sphincter. Pig. 7. View of the same from above. Pig. 8. Pront view, showing upper branches of the retractors, which are attached to the wall of the tube and to the disc, M" and M'. THE FEKTILIZATION OF FLO WEEING PLANTS. BY J. T. ROTHROCK. It is now universally accepted by botanists that there exist distinct sexes in the vegetable kingdom, and that na- ture's method of maintaining the existence of a specific form, is to bring the male and female elements in con- tact. In a normal flower, the first group of organs we find inside the corolla, are the stamens ; while the yellow powder, so frequently found inside of the swollen ends (anthers) , is the pollen or male element. In the centre OF FLOWERING PLANTS. 65 of the flower we usually find one or more organs, called the pistil or pistils. The end or edge of this organ is called the stigma, which is generally more or less viscid. It is upon this viscid stigma that the pollen falls, or is conveyed by insects, the wind, or other agents. Soon a small tubule shoots out from the pollen grain ; this tubule grows down through the stigma and style, into the ovary, where it comes in contact with the unfertilized ovule, which is then fertilized, and. becomes capable of develop r ing in its cavity an embryo that in time, and under favor- able conditions, will become a perfect plant. In by far the greater number of flowering plants, we find both the male and female element in the same flower, or, in other words, such plants arc hermaphrodites. One would nat- urally suppose that there could be but one object in thus placing the sexual elements in such immediate juxtaposi- tion, namely, that each pistil might be fertilized by its own pollen or male element. Late researches have, however, made it evident that often even among plants, the nup- tials cannot be celebrated without the intervention of a third party to act as a marriage priest, and that the oiSce of this third person is to unite the representatives of dif- ferent households. To be specific, seed capsides are- most productive when their ovules are fertilized by pollen from another plant, or flower of the same plant. " Breeding in and in," can by absolute experiment, be proven to pro- duce a degenerate offspring in the vegetable kingdom, no less than in the event of a marriage between first cousins in the human race. Now the marriage priests who officiate in the vegetable kingdom are insects in search of honey ; the winds, or anything which by accident, or design, may carry the pollen from one flower to another. How often do we AMERICAN NAT. VOL. I. 9 66 THE FERTILIZATION hear our agricultural friends complain, that they cannot succeed in keeping pure some choice varieties of vege- tables, in consequence of the pollen from some common stock being wafted or carried to the pure variety, and thus contaminating it ? Mr. Darwin has lately proven in the case of the genus Linum, or Flax, that though the stigma of a flower be completely dusted over with its own pollen, not que seed will be matured. This certainly was a "cap- ital experiment." Though the impotency of pollen when applied to its own stigma is absolute in this case, we may not infer the line is always so sharply drawn. Facts con- tradict this ; but a great step will have been taken in the right direction if we are taught to question many so-called instances of close fertilization. For example, most of us are familiar with the general habit of our common Laurel (Kalmia). We remember, also, that when in bloom, it shows us a waving sea of beautiful, rose-colored flowers, growing so clogely together as to almost hide the leaves from view. When the flower first opens, we may observe that there is one small pocket in each angle of the flower, and that toward each of these pockets is bent backwards a stamen, so that an anther is included in each pocket. Every stamen represents a spring just ready to fly to a natural position of rest, when let loose. An insect in search of nectar lights on the flower, and in so doing jars the flower sufficiently to cause the stamen to spring up and converge over the stigma. Here, at once we say, the design is close fertilization. But not so fast. Pollen is often carried by the force of the spring to the pistil of an adjacent flower ; and remembering the lesson taught us by the flax, we are not sure that pollen of one flower may not be prepotent when applied to the stigma of another flower, and so completely destroy close fertilization. We OF FLOWERING PLANTS. 67 do not say it is prepotent; any reader of the "Natural- ist" may experiment for himself on the Kalmia. It is only offered here as a hint. The field opened up by Mr. Darwin's experiments is new, and alluring, and perchance for that very reason may sometimes be so attractive as to lead us beyond the limits of sound reasoning, and reliable experiments. Yet there exists a group of plants in the study of which we may almost feel safe in giving a loose rein to our theories, for facts already ascertained, prepare us to believe noth- ing can be too strange to be true, in relation to the fertil- ization of this group. I allude to the so-called dimorphic plants ; where the same species presents two distinct forms, one with long stamens and short pistils ; the other with short stamens and long pistils. Now it has been proven in the case of the Flax, and of the Primrose, that the most fertile union is that which results from the im- pregnation of the long-styled forms by the pollen of the short-styled, and the reverse. Some experiments made by myself, at the suggestion of Prof. Asa Gray, convince me that the same applies in a remarkable degree to our common little Spring Beauty ( Oldenlandia) , or, as it is commonly called, Innocence oi\ Bluets.* This differentiation of the specific form, may even go farther, and give us trimorphic plants. I cannot better il- lustrate what I mean, than by quoting at length, though at second hand, from Mr. Darwin's paper, "On the Sex- ual Relations of the three forms of Lythrum salicaria." *In Oldenlandia we find an evident structural differentiation of both pollen and stigma. The relative length of the stamens of one form when compared with that of the style of the other form, almost drives one to the conclusion that the design, in this case, is to secure cross- . fertilization. I have frequently observed a species of Thrips crawl- ing about from flower to flower, with its back completely dusted over with pollen. 68 THE FERTILIZATION? "InLythrum salicarja (Spiked Loosestrife) three plain- ly distinct forms occur ; each of these is an hermaphro- dite ; each is distinct in its female organs from the other two forms ; and each is furnished with two sets of stamens or males, differing from each other as much as if they be- longed to different species ; and if smaller functional dif- ferences are considered, there are five distinct sets of males. Two of the three hermaphrodites must co-exist, and the pollen be carried by insects reciprocally from one to the other, in order that either of the two should be fully fertile ; but, unless all three forms co-exist, there will be a waste of two sets of stamens, and the organization of the species as a whole will be imperfect. On the other hand, when all three hermaphrodites co-exist, and the pollen is carried from the one to the other, the scheme is perfect ; there is no waste of pollen and no false co-adaptation. In short, nature has ordained a most complex marriage ar- rangement, namely, a triple union between three hermaph- rodites, each hermaphrodite being in its female organ quite distinct from the other two hermaphrodites, and partially distinct in its male organs, and each is furnished with two sets of males." It farther appears, "that only the longest stamens fully fertilize the longest pistils, the middle stamens the middle pistil, and the shortest stamens the shortest pistil. And now we can comprehend the meaning of the almost exact correspondence in length between the pistil of each form, and the two half dozen sets of stamens borne by the two other* forms ; for the stigma of each form is thus rub- bed against that spot of the insect's body, which becomes most charged with the proper pollen." Mr. Scott has led us to adopt a new clause in our sci- entific creed, and one, which, did it not come properly OF FLOWERING PLANTS. 69 vouched for, might well cause a rising doubt. He tells us that the pollen of one species of Passion Flower will fertilize the ovules of another species, though the ovules of the first may not in turn be fertilized by the pollen of the second. Thus Tacsonia mollissima will fertilize the ovules of Passiflora racemosa, but Passiflora will not fer- tilize Tacsonia. Interesting as may be the means resorted to in the ca- ses above mentioned, to secure cross-fertilization (mostly through the medium of insects) they yield in fascination to the adaptations by which the same results are accom- plished by the same agents in many Orchids. We must refer those who wish to go into the details of fertilization, as it is brought about in this gorgeous family, to Mr. Darwin's interesting volume on "Fertili- zation of Orchids by Insects." They will there find the subject treated of by a master mind in such inquiries. The temptation to meddle in work so much better done elsewhere, is too great, and we should be surprised at ourselves if we passed the subject entirely by. Among the Orchids and Milkweeds (Asclepias) , we find that the pollen, in place of being loose, or at the most slightly coherent, is here neatly done up in two' small decanter- shaped packets, which are connected at the top of the necks by a small, viscid gland. Let us imagine that on some bright summer morning, a humble bee, for example, happening to be out in search of the material from which to get its store of honey, alights on one of these Orchids. Standing, perchance, on the large lip (so prominent among these flowers), it dips its head down to the bottom of the flower in search of nectar. The chances are ten to one that its forehead strikes directly upon this viscid gland connecting the two 70 THE FERTILIZATION packets of pollen. By the time the nectar is exhausted the gland has become adherent to the bee's head, and as it (the head) is withdrawn, the two pollen masses are extracted from their pockets, and now stand off in front like a pair of horns. The bee, most likely, flies to another plant of the same species, or still more probably to another flower of the same plant. Suppose the stigmatic surface of this species of plant be broad, or possibly separated almost into two parts ; we will find the packets have slowly but surely diverged so as to be the exact width of that surface. Suppose on the other hand, the stigma be a narrow one, we shall find that the packets have come close together. In either case when the bee's head bobs down into the next flower, it will almost certainly happen that these same pollen masses will be left sticking on the stigma when the bee leaves, or at least part of the pollen will be left. These masses of pollen have long since been frequently observed on the bee's head, but, until quite lately, no meainng had been attached to it. Some ento- mologists, I believe,' have even been guilty of describing these as natural appendages to the bee's head. So mani- fest are these adaptations for the purpose of cross fertil- ization among Orchids, that we may be well nigh sure some great purpose is to be subserved. Perhaps it would not be too much to say, that but for insect agency many Orchids would become extinct. There are not wanting those who even affirm the insect shape assumed by some Orchidaceous flowers, has no less purpose than to serve as a decoy, and thus tempt the bee or butterfly to alight upon them and accomplish the work of fertilization. Those wishing to be apprized of the mode of fertilization, as it occurs in our American plants, will find some admirable arti- cles from the pen of Prof. Asa Gray, in Silliman's Journal OF FLOWERING PLANTS. 71 for 1862. Kobert Brown long since called attention to insect agency, in the fertilization of the Milkweed family. Almost any summer day we may repeat his observations for ourselves. So adhesive are the glands of the Ascle- pias obtusifolia (Wavey-leaved Milkweed) , that we often find honey bees unable either to withdraw the packets, or loose their feet from the gland, and thus they become prisoners for life. There exists yet another class of dimorphic flowers, in which we find the large and more conspicuous flowers less fertile than those of the other form, which are arrested in their development, and are fertilized in the bud. Hugo van Mohl has of late called especial attention to them. Such flowers have been happily termed precociously fer- tilized. Mohl concludes, after close examination of Viola, Oxalis, Specularia and Impatiens, that nature is here specially solicitous to secure close breeding, or that each flower shall be fertilized by its own pollen. He calls attention also to the fact, that in the large anthers of the smaller form of Oxalis acetosella, not more than two dozen pollen grains are found, while in the anthers of the larger form they are much more numerous. In the smaller form, however, the few grains are made more potent, and the exercise of their function is secured, by being placed in contact with the stigma. It results, however, that our list of closely fertilized plants is becoming smal- ler, under the repeated observations of accurate investiga- tors, and that, what was supposed to be a special adapta- tion to secure close fertilization, is, after all, but a more nicely conceived method of obtaining an opposite result. For example, we were formerly taught that the interior petals of Corydalis clasped the anthers and stigma of the flower in so tisrht an embrace that outside fertilization 72 THE FERTILIZATION OF FLOWERING PLANTS. was a thing not to be thought of. Dr. Hildebrand in- forms us however, that though the stigma of Corydalis cava be completely dusted over with pollen from the same flower, yet no seed will set if insects be excluded from carrying pollen from flower to flower. This fact is, as will be observed, another illustration of Mr. Darwin's law of prepotency of pollen taken from one flower, and applied to another. Professor Gray also calls attention to the "effectual activity of so large an insect as the bumble-bee in fertilizing our Corydalis aurea" (Golden Corydalis) . Just now we can point to but one instance in which a plant of high order is found to produce perfect embryos, without the ovules having been previously fertilized ac- cording to the known method. In the Kew Gardens, near London, has been kept for many years a plant of the Spurge family, which furnishes this one example. Dr. Hooker writes to Humboldt concerning it, as follows : "Our Ccelebogyne still flowers with my father at Kew, as well as in the Garden of the Horticultural Society. It ripens its seeds regularly. I have repeatedly examined it with care, but have never been able to discover a pene- tration of pollen utricles into the stigma, nor any traces of their presence in the latter or in the style." This plant belongs to the old Linnsean class Dioecia. It is unisexual, and as there exists only (so far as known) the female plant in England, it is difficult to conceive how the fertil- ization is accomplished, unless through the agency of concealed anthers. Though diligent search has been made time and again for the anthers, they do not seem to have been found. "We may still fairly hesitate before accepting this as an example of parthenogenesis, or virgin fertility.